1. Field of Invention
The present invention is broadly concerned with methods of forming antireflective coating layers on silicon and dielectric materials as well as the resulting integrated circuit precursor structures. More particularly, the inventive methods comprise providing a quantity of a polymer generated by the subliming of monomers into the plasma state by electric current and subsequent polymerization thereof onto the surface of a substrate.
2. Background of the Prior Art
Integrated circuit manufacturers are consistently seeking to maximize silicon wafer sizes and minimize device feature dimensions in order to improve yield, reduce unit case, and increase on-chip computing power. Device feature sizes on silicon chips are now submicron in size with the advent of advanced deep ultraviolet (DUV) microlithographic processes. However, reducing the substrate reflectivity to less than 1% during photoresist exposure is critical for maintaining dimension control of such submicron features. Therefore, light absorbing organic polymers known as antireflective coatings are applied beneath photoresist layers in order to reduce the reflectivity normally encountered from the semiconductor substrates during the photoresist DUV exposure.
These organic antireflective layers are typically applied to the semiconductor substrates by a process called spincoating. While spincoated antireflective layers offer excellent reflectivity control, their performance is limited by their nonuniformity, defectivity and conformality constrictions, and other inefficiencies inherent within the spincoating process. As the industry approaches the adoption of eight-inch or even twelve-inch semiconductor substrates, the inherent inefficiencies of the spincoating process become magnified.
When spincoated at thicknesses ranging from 500 Å to 2500 Å, commercial organic antireflective coating layers require polymers specifically designed to prevent molecular intermixing with adjacent photoresist layers coated and baked thereon. Although high optical density at DUV wavelengths enable these pre-designed polymers to provide effective reflectivity control at prior art dimensions, they have numerous drawbacks.
Another problem with the currently available antireflective coating application processes is inadequate planarization. Organic antireflective coatings are usually formed by spincoating. The formed layers typically lack uniformity in that the thickness at the edge of the substrate is greater than the thickness at the center. Furthermore, spincoated antireflective coating layers tend to planarize or unevenly coat surface topography rather than form highly conformal layers (i.e., layers which evenly coat each aspect of the substrate and the features). For example, if an antireflective coating layer with a nominal layer thickness of 1000 Å is spincoated over raised features having feature heights of 0.25 μm, the layer may prove to be only 350 Å thick on top of the features, while being as thick as 1800 Å in the troughs located between the raised features. When planarization occurs with these ultramicroscopic feature sizes, the antireflective coating layer is too thin on the top of the features to provide the desired reflection control at the features. At the same time, the layer is too thick in the troughs to permit efficient layer removal during subsequent plasma etch. That is, in the process of clearing the antireflective coating from the troughs by plasma etch, the sidewalls of the resist features become eroded, producing microscopically-sized—but significant—changes in the feature shape and/or dimensions. Furthermore the resist thickness and edge acuity may be lost, which can lead to inconsistent images or feature patterns as the resist pattern is transferred into the substrate during subsequent etching procedures.
Other problems can occur as well due to the fact that spincoating of these ultra-thin antireflective coating layers takes place at very high speeds in a dynamic environment. Accordingly, pinholes, voids, striations, bubbles, localized poor adhesion, center-to-edge thickness variations, and other defects occur as a consequence of attendant rapid or non-uniform solvent evaporation, dynamic surface tension, and liquid-wavefront interaction with surface topography. The defects stemming therefrom become unacceptable with increased wafer size (e.g., eight- to twelve-inch wafers) and when patterning super submicron (e.g., 0.25 μm or smaller) features.
There is a need for an improved process of depositing antireflective coatings on various substrates. This process should overcome the above-mentioned drawbacks while providing for rapid deposition of the antireflective coatings.